The invention relates generally to a liquid ink printer and, more particularly, to a curved infrared foil heater which is used to dry images formed on a recording medium in a liquid ink printer.
Liquid ink printers of the type frequently referred to as continuous stream or as drop-on-demand, such as piezoelectric, acoustic, phase change wax-based or thermal, have at least one print head from which droplets of ink are directed towards a recording medium. Within the print head, the ink is contained in a plurality of ink channels. Power pulses cause the droplets of ink to be expelled as required from nozzles at the end of the ink channels.
In a thermal ink jet printer, the power pulse is usually produced by a heater transducer or a resistor, typically associated with one of the ink channels. Each resistor is individually addressable to heat and vaporize ink in the ink channels. As voltage is applied across a selected resistor, a vapor bubble grows in the associated ink channel and initially bulges from the channel nozzle followed by collapse of the bubble. The ink within the ink channel then retracts and separates from the bulging ink thereby forming a droplet moving in a direction away from the channel nozzle and towards the recording medium whereupon hitting the recording medium a dot or spot of ink is deposited. The ink channel is then refilled by capillary action, which, in turn, draws ink from a supply container of liquid ink.
The ink jet print head is typically incorporated into a carriage type printer which has a relatively small print head containing the ink channels and nozzles. The print head can be sealingly attached to a disposable ink supply cartridge. The combined print head and cartridge assembly is attached to a carriage which is reciprocated to print one swath of information (equal to the length of a column of nozzles), at a time, on a stationary recording medium, such as paper or a transparency. After the swath is printed, the paper is stepped a distance equal to the height of the printed swath or a portion thereof, so that the next printed swath is contiguous or overlapping therewith. This procedure is repeated until the entire page is printed.
Many liquid inks and particularly those used in thermal ink jet printing, include a colorant or dye and a liquid which is typically an aqueous liquid vehicle, such as water, and/or a low vapor pressure solvent. The ink is deposited on the paper to form an image in the form of text and/or graphics. Once deposited, the liquid component is removed from the ink and the paper to fix the colorant to the paper by either natural air drying or by active drying. In natural air drying, the liquid component of the ink deposited on the paper is allowed to evaporate and to penetrate into the paper naturally without mechanical assistance. In active drying, the paper is exposed to heat energy of various types which can include infrared heating, conductive heating and heating by microwave energy.
Active drying of the image can occur either during the imaging process or after the image has been made on the recording medium. In addition, the recording medium can be preheated before an image has been made to precondition the recording medium in preparation for the deposition of ink. Preconditioning of the recording medium typically prepares the recording medium for receiving ink by driving out excess moisture which can be present in a recording medium such as paper. Not only does this preconditioning step reduce the amount of time necessary to dry the ink once deposited on the recording medium, but this step also improves image quality by reducing paper cockle and curl which can result from too much moisture remaining in the paper.
Slow to medium drying inks are currently used in most ink products and printers to provide for optimum print quality for black to achieve performance comparable to xerographic toner images. These slow to medium inks typically take 45-60 seconds to dry at ambient environment by natural air drying. Drying times over a wide variety of recording media in stress environments can be driven under 5 seconds with the use of an active dryer.
A planar thin foil heater has been used in the prior art to actively dry deposited ink on the recording medium. Unfortunately, these thin foil heaters suffer from wrinkling on the surface due to non-uniform thermal expansion during heating. Wrinkling of the thin foil heater surface causes uneven heating and drying of the ink on the recording medium.
Other disadvantages to thin foil heaters include undesirable heatsinking or heating of other printer components due to conduction of heat away from the foil heater through its mounting structure.
U.S. Pat. No. 5,742,315 to Szlucha et al., commonly assigned as the present application and herein incorporated by reference, uses a spring attached to one end of the foil heater to self-tension the flat heater foil to prevent wrinkling of the foil heater due to thermal expansion of the heater foil.
U.S. Pat. No. 6,231,176 to Peter, commonly assigned as the present application and herein incorporated by reference, uses a bowed leaf spring to self-tension a flat foil heater to prevent wrinkling of the heater foil due to thermal expansion of the heater foil.
It is an object of the present invention to provide a non-spring means to self-tension a foil heater to prevent wrinkling.
It is another object of the present invention to provide a curved foil heater to self-tension to provide a wrinkle-free heating surface opposite the print head for active drying deposited ink on the recording medium.
According to the present invention, there is provided an ink jet printing machine for printing liquid ink images on a recording medium moving along a recording medium path through a printing zone. The printing machine includes a print head for image-wise depositing liquid ink droplets on the recording medium; and a curved foil heater, disposed adjacent to the recording medium path opposite the print head, for heating the recording medium to dry the image-wise liquid ink droplets. The foil heater is an infrared emitting, etched foil circuit heater mounted within a channel in a frame to curve and thus self-tension to prevent wrinkling of the foil heater despite any thermal expansion of the foil heater.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.